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    Check device online
    1. Home
    2. Serial port

    Web Serial Test

    ConnectionSelect a preset or enter the serial port parameters used by your device.Disconnected
    Device preset
    Flow control
    Port parameters

    Serial terminal

    1. Connect a serial device to start.
    Commands are sent directly to the device and may change settings, move hardware, erase data or start firmware operations.
    0 BReceived0 BSent0 B/sAverage receive rate
    Diagnostics and control lines

    Control signals

    CTSDSRDCDRI

    Changing DTR or RTS can reset, boot or otherwise affect some devices.

    Loopback test

    Disconnect the device from other circuits, connect TX to RX, then run the test. A 256-byte pattern is sent and compared with the echo.

    Online Web Serial terminal and port test

    This tool connects to serial devices directly from the browser. It works with development boards, USB-to-UART adapters, 3D printers, GNSS receivers, modems and other devices that expose a serial port. No desktop program is required.

    How to test a serial device

    1. Connect the device and close Arduino IDE, PuTTY, CoolTerm or any other program that may be using its port.
    2. Select a preset or enter the baud rate, data bits, parity, stop bits and flow control.
    3. Choose the port in the browser permission dialog.
    4. Read data in UTF-8, HEX or ASCII mode, then send commands only after checking the device documentation.

    Popular compatible devices

    Common examples include Arduino Uno, Nano and Mega boards, ESP32 and ESP8266 boards, Raspberry Pi Pico, BBC micro: bit, CP210x, CH340 and FTDI USB-to-UART adapters, Marlin-compatible 3D printers, GPS/GNSS receivers and AT-command modems. The correct driver must expose the device as a serial port in the operating system.

    What the loopback test measures

    A wired loopback connects TX to RX. The test sends a known 256-byte pattern and compares the returned bytes to show missing, mismatched or extra bytes and the effective receive rate. Do not run it while the adapter is connected to another active circuit.

    Frequently asked questions

    Which browsers support this Web Serial test?

    Use desktop Chrome or Edge 89+ or Firefox 151+ on Windows, macOS or Linux. Mobile Firefox, Safari, iPhone and iPad are not currently supported.

    Why is my serial device missing or busy?

    Install the device driver when required and close Arduino IDE, PuTTY, CoolTerm and other applications that may already have the port open. Then reconnect the USB cable and try again.

    Do I need to connect TX and RX for the loopback test?

    Yes. A hardware loopback returns transmitted bytes to the receiver. Isolate the adapter from other circuits first; never short signal pins to power or ground.

    Does the website upload data from my serial port?

    No. Serial input and output are processed locally in the tab. Settings and recent commands are stored in localStorage; received data is not saved unless you explicitly export the log.

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